Electric spark plug or the like for internal combustion engines



Feb. 22, 1938. H. G. BORNEMANN ELECTRIC SPARK PLUG OR THE LIKE FOR INTERNAL COMBUSTION ENGINES Filed April 17, 1935 Walled.

Mica,

flulaif'iug Manerial wm, mm! T reads Patented Feb. 22, 1938 ELECTRIC SPARK PLUG OR THE LIKE FOB INTERNAL COMPUSTION ENGINES Hermann Georg Bornemann, Zehlendori-Kiein Machnow, Germany Application April 17, 1935, Serial No. 16,845

- In Germany April 17, 1934 16 Claims.

This invention relates to an arrangement for regulating, in given cases automatically, the working temperature of electric spark plugs or electrically heated ignition tubes.

As. is known, it is endeavoured to construct the electric'spark plugs of internal combustion engines in such a manner that the insulating body does not exceed a certain temperature when the 'engine is running, because otherwisethere is a danger of premature ignition. This danger will occur when the insulating body attains a temperature of approximately 600 C. On the other hand, the insulating body must not be cooled below a certain temperature because otherwise soot bridges. are formed on this portion bydeposits trom the gases from combustion, on which bridges the voltage of the spark plug can passfrom one pole to the other without, attaining the object oi the ignition. As a rule; it is endeavoured to maintain the insulating body at a medium teuiperature of 350 to 400 C. at which automatic cleaning-that is the prevention of the formation of soot br'idgesis still to be'expected.

The temperature of the insulating body is primarily influenced by the heat development 'of the engine, that is from its thermic properties and its manner of working; the tendency for the temperature to raise increases'with the higher thermic properties of the engine and becomes greatest for example in the case when running under ,tull load with supercharging. The temperature of the insulating body depends in the second place upon the construction of the spark plug, that is ,the possibility of absorbing heat on the one hand insulator must be"as small aspossible in view.

and giving up heat on the other hand. The lower the thermic value of the engine for which the spark plug is intended, the greater must be the heat absorbing surface (base surface) of the insulator, in order to reliably prevent jumping of the spark and to maintain the automaticcleaning temperature. If, however, the thermic value of the engine is particularly high, the foot of the of the danger of premature ignition. At the same timeit is necessary to provide for an eiIect-, ive heat radiation in the event of increase oi! the influences tending to .raise the temperature;

' This necessitates the provision of a relatively large surface onthe'head of the insulating body,

spark plug of certain shape is restricted to a small range of thermic conditions. Although it is possible to meet the practical requirements of difierent engines in this manner by providing a sufllcient number of different types of spark plugs, the known plugs are nevertheless. always open to the objection that they can only approximately bechosen for a medium thermic value of the-engine which, however; actually may vary within wide limits between no-load and iull load. 10

The object of the invention is to extend the thermic range of the spark plug so that a single a, type of plug can be employed'tor diflerent kinds of engines. This is attained by means which enable the plug to be adjusted to themo'st favour- 15 able prescribed working temperature'both tor a high and low thermic value of the engine. Thus premature ignition by overheating in consequence of overloading of the engine and creeping caused by great drop of temperature when the .engine is idling for a long time are prevented tov a great extent. This eflect can be improved according to a modification of thein-vention by anarrangement by means of which the plug is automatically adjusted to themost favourable working temperature in the event of changes in the heat conditions.

The thermic range can according to the invention be extended by making the insulating .body of the spark plug of a material possessing a particularly great heat conductivity and providing its head or other radiating portion with an arrangement which enables the radiating surface to be more ,or less covered. Theidea is that, ii an insulating material is employed-possessing a particularly I ceeding that of, the known spark plugs, the heat passage to the surrounding metal mass and tothe atmosphere will become soleflective that the insulating body of the spark plug can be made I with a relatively large base surface without its 40 becoming too hot when fitted in a high power motor. The large insulating base also ensures a suflicient distance of insulation in-the event of idle running. The large insulating, base-likewise reduces the dangerof 'sooting or clogging ing thedesired working temperature from being so lowered. The head of the insulating body is preferably provided with cooling ribs 0! diskor helical form forthe pumflc'oiincreasing the size of the radiating surface, whereas the size of this canbevariedinanw highhe at conductivity ex- 35 eifective manner by slipping a cap-more or less over the ribbed portion. In the case of automatic regulation this cap is automatically adj ed by a thermostatic element influenced by tiie actual heat of the insulating body.

In order'to attain a particularly good heat conductivity of. the insulating body it is proposed to make the same of alternate thin layers of a metal, such as aluminium, and an insulating material, such as mica, so that the heat can flow freely in the metal in the axial direction of the insulating body from the base to the radiating surface, whereasthe voltage is prevented from surface thus treated has a considerably greater ability for absorbing and radiating heat, whilst at the same time affording greater resistance against electrical piercing.

, Edie inve tion also presents advantages in the casehf ignition tubes for-oil engines. The known tubes are generally hollow metal bodies with an insulated projecting heating coil which is maintained at glowing temperature by the heat from combustion but which must be brought to the necessary-temperature by electric heating when starting up the engine. In this case the .drawback also arises that one and the same plug is mostly not suitable for difierent thermic conditions. If the conditions for leading off the heat are such that the ignition takes place reliably at low external temperatures, there is a danger of the ignition body becoming overheated and the heating coil destroyed in the event of higher temperature conditions and when running for a.

long time under heavy load. This often occurs when the load is not even full-load. This drawback can likewise be overcome by providing the ignition tube with a radiating surface fitted outside the cylinder, the effect of which being adjustable by a movable cover. According to the invention a projecting head with cooling ribs of good insulating. material, preferably aluminium, is provided on the plug and a cap of I bad insulating material is adjustably supplied over this head, the'adjustment being, if desired,

- efiected automatically with the aid of a thermowith automatic regulation,

static member. The heatabsorbing base of the ignition tube which accommodates the heating spiral may be made of pure aluminium, but it is advisable in this instance to electrically oxidize the surface to obtain a better heat absorption and chemical resistance.

Several embodiments of the invention are illustrated by way of example in the accompanying drawing in which: v

-Fig. 1 shows in longitudinal section a spark plug with hand adjustable cover cap,

Fig. 2 is a cross section through the upper end of the plug on line 2-2 of Fig. 1,

' Flg.- 3 is a part-longitudinal section of a" plug Fig. 4 shows on a larger scalea portion of Fig. 5 is an elevation partly in longitudinal section of an insulating body,

. possessing a particularly high heat conductivity,

and c the middle electrode which is cemented in the insulating body. The base and collar of the insulating body are of the usual construction, whereas the head d is provided with cooling ribs extending in the form of a screw thread. A cap 2 is screwed on to this screw thread and covers the head, this cap being made of material possessing a low heat conductivity such as asbestos slate, glass, porcelain or artificial-resin. According to the position of the cap a greater or lesser portion of the head surface is prevented from radiating so that the heat radiation can be varied within wide limits and consequently the plug adapted to the actual thermic conditions of the engine. The middle electrode 0 is packed at its upper end against the insulating body preferably by means of a soft elastic disk 1, for example of aluminium, which disk is held in position by a circular nut g. A spring h clamped on the nut 9 serves for securing the cap in its adjusted position. This spring consists for example of a resilient ring pressed in oval shape and bent over in its twomiddle portions. The loop shaped ends of this spring engage in recesses on the inner side ofthe cap (Fig- 2).

In the form of construction shown in Fig. 3 the head d of the insulating body is provided with disk-shaped cooling ribs on which the cap 6 slides. The adjustment of the cap is effected in this instance automatically by means of a thermostatic element which regulates the working temperature of the sparkplug to the prescribed value. This arrangement presents the advantage that the radiating surface is automatically varied in size when the heat conditions fluctuate. In the example illustrated in the drawing a pair of bi-metal springs is shown as regulating element. in position on the insulating body at one end by nuts g andg", whereas its other end is clamped to the cap e by means of the bent over edge of a small sleeve is which serves at the same-time This element is secured as guide for the cap. The outer edges of the cooling ribs are preferably rounded as shown in Fig. 4 so that the cap flange e, bearing against at least two ribs, is guided at this point with very I d of the head carrying the cooling ribs is made of solid metal and slipped on to the inner portion in the manner illustrated in Fig. 5.

The layers may be produced in a simple manner by winding a mica band varyingin width for the purpose of producing the final shape of the insulating body. A portion of such a band is il'-' lustrated on enlarged scale in longitudinal section in Fig. 6. The mica layers 1 may be about 3 mm. in thickness and on these layers aluminium strips m of about the same thicknessare stuck or cemented transversely to the longitu dinal direction'oi' the band and mutually displaced on the two sides of the band. By this means the .metal layers in the finished wound body extend continuously from one end to the other in longitudinal direction, whereas the metal the metallayers by full lines.

cores are interrupted and insulated from one another -by the mica layers in the transverse direction. Fig.- 7 shows diagrammatically a portion of the wound base of the insulating body, the

mica layers being indicated by broken lines and The electrode pin is first surrounded by a casing composed of several mica layers. The band constructed in the manner illustrated in Fig. 6 is then wound about this casing, and the end of this band extends 'at an incline in order to produce the conical shape of the base portion. As can be seen from Fig. 7 the metal layersdo not extend right down to the edge of the mica band in order to prevent the voltage from creeping over at this point. -A further protection is efiectedby providing each aluminium layer with the above mentioned oxidized coating which possesses agood insulating property and at the same time improves the heat transmission. Finally the small gaps between the mica layers on the surface of the body thus wound are preferably filled with a strong insulating cement which smooths the surface. Pulverized asbestos mixed to apaste with waterglass which may also be employed for cementing the aluminium layers on the mica band has been found suitable for this purpose. If the whole mass after having been wound is heated to a temperature of 150 to 200 C. a body is formed p'os-- essing great mechanical strengt and insulating properties and having an excellent heat'conductivity.

The'body produced in this mann'er is particularly suitable for the following reasons; Sintered corundum is known as the insulating material possessing the best heat conductivity. It pos- .sesses a heat conductive coefilcient of about 16.8.

(caIsX mtn/sq.mtr. hr. (2.), that is 14 times the conductive capacity of steatite. 'The corre- 'sponding coemcient for aluminium is 165, and

' for electrically oxidized aluminium slightly lower.

Ignoring "the relatively lowconductivity of the mica which is 0.3, a heat conductive'coefiicient of about 80 can be reckoned for a mixed insulating 45' material consisting approximately of 50% aluminium. This is about 5 times that of sintered corundum and 75 times that of steatite. The heat absorbed by the insulating body is therefore con- 'ducted in a very effective manner to the ribbed portion of the body, and the radiation from the rial such ass-pulverized mica mixed with a bind ing medium, the whole being moulded under pressure to the desired shape.- The metal threads nhmay be in the form of a coiled wire netting or in the form of loose metal wool. In this latter instance the body must be inclosed on the inner and outersldes-by a shell p of pulverized mica.

. It is evidentlyalso possible to arrange a plurality of metal tubes of different diameters concentricallyone within the other and to 1111 the gaps between these tubes with pulverized insulating material mixed with a binding medium.

In all instancesit is essential that the metal inserts of the insulating body are in conductive .connection withia large slu'face of good radiating 'material, for example in the form of a ribbed sleeve d such as illustratedin Fig. 5.

. l. The thin protecting layer q (Fig. 7) formed of the abovementioned .cement like substance on ed to automatically actuate said means.

the surface of the base of the. insulating body also has a particularly favourable effect. This layer formed for example oiF-waterglass and asbestos powder possesses the property of good permeability for heat radiation, whereas it is a bad con- 5 ductor of convective heat. As this thin layer is connected with good conductive metal veins uniformly distributed'on itsrear side the insulating body attains the necessary temperature very quickly when starting up because for this purpose only the accumulation of a relatively small quantity of heat in the coating layer is required. On the other hand the metal veins in. a certain sense .feel off the whole rear side of the thin layer and conduct the heat to the ral5 diating surface at a speed increasing corresponding to the increase of temperature drop between the base and the head, and thus prevent the permissible temperature from being exceeded. This efiect constitutes an extensive automatic regulation of the temperature conditions so that a relatively slight subsequent regulation by varying the radiating surface is sumcient, or this subsequent regulation may possibly even be entirely dispensed Lwith if the thermic working range of the plugzii is not required to deal with all occurring working conditions.

What Iclaim as new and desire to secure by Letters Patent of the United States, is: a

l. A spark plug,- comprising in combination, a 80 metal casing forming the outer electrode, an

insulating body inserted in and projecting from. the said casingto form a radiating surface and having an axial bore, a metal pin extending through said bore and forming the 'inner .elec- 88 tion of said insulating body to increase the area of said radiating surface, a metalpin extending through said bore and forming the inner electro de, sa.id insulating body consisting of a material having high heat conductivity, and means on the ribbed end of said insulating body for ad-.

justing the exposed area of the radiating surface.

3. A spark plug,.comp'rising in combination, a metal casing forming the outer electrode, an insulating body inserted in and projecting fromthe said casing to form 'aradiating surface and having an. axial bore, a metal pin extending through said bore and forming the inner electrode, said insulating body consisting of a mate- J rial having high heat conductivity, and a cap shi'ftable on the projecting end of said-insulating body to adjust the exposed area' of the radiating surface.

4. A spark plug, comprising in combination, a metal casing forming the outemelectrode, an insulating bodv inserted in and projecting from the 1 said casing to form a radiating surface and having an axial bore, a metal pin extending through said bore and forming the inner electrode, said insulating bo'dy consistingof a material having high heat conductivity means .on the projecting end of said insulating body for adjusting the exposed area of the radiating surface, and a thermostatic member between the projecting end of said. insulatingbody and said adjusting means adapt- V a 75 good radiating material slipped on to the projecting portion of said body, and means on said sleeve for adiusting the exposed area of the radiating surface.

6. A spark plug, comprising in combination, a metal casing forming the outer electrode, an insulating body inserted in and projecting from the said casing to form a radiating surface and having an axial bore, a metal pin extending through said bore and forming 'the inner electrode, said insulating body consisting-of a material having high heat conductivity, an aluminium sleeve having an electrically oxidized surface slipped on to the projecting portion of said body, and means on said sleeve for adjusting the exposed area of the radiating surface.

'7. A spark plug, comprising in combination, a metal casing forming the outer electrode, an insulating body inserted in and projecting from the said casing and having an axial bore, .a metal pin extending through said bore and forming the inner electrode, said insulating body consisting of ,an'electrically insulating mass with good conduetors of heat extending therethrough and forming a continuous connection between the base andthe projecting portion of the body, a large radiating surface surrounding the said pro, jecting end and in contact with the said conductors, and means on the projecting end of said insulating body for adjusting the exposed area of the radiating surface.

8. A"spark plug; comprising in combination,-a metal casing forming the outer electrode, an insulating body inserted in and projecting from the said casing and having an axial bore, a metal pin extending through said bore and forming the inner electrode, said insulating body consisting of metal threads embedded in a' compressed substance composed of powdered insulating material with a binding medium, said metal threads forming a continuous connection between the base and the projecting portion of the body, and a large. radiating surface surrounding the said projecting end and in contact withthe said metal threads.

9. A spark plug, 'comprising'in combination, a metal casing forming the outer electrode, an' insulating body inserted in and projecting from the said casing and having an axial bore, ametal pin extending through said bore and forming.

the inner electrode, said insulating body consisting of metal wool embedded in a compressed substance composed of powdered insulating material with a binding medium and being covered on its inner and outer sides by an insulating layer, said metal wool forming a continuous connection between the base and the projecting portion ofthe insulating body inserted in and projecting from the said casing and having an axial bore, a metal pin extending through said bore and forming the inner electrode, said insulating body consisting of a plurality of concentrically arranged metal inserts embedded in a compressed substance com- 3 posed of powdered insulating material with a binding medium, said metal inserts forming a continuous connection between the base and the projecting-portion of the body, and a metal sleevewith a ribbed surface slipped on to the said projecting portion and being in contact with the said metal inserts.

"11. A spark plug, comprising in combination, a metal casing forming the outer electrode, an insulating body inserted in and projecting from the said casing and having an axial bore, a metal pin extending through said bore and'forming the inner electrode, said insulating body consisting of an electrically insulating mass with good conductors of heat extending therethrough and forming a continuous connection between the base and the projecting portion of the body, a

large radiating surface surrounding the said projecting end and in contact with the said conductors, and a thin coating of a heat accumulating cement covering the outer surface of the base; portion of the insulating body and being in contact with the said conductors of heat.

. 12. A spark plug, comprising in combination, a metal casing forming the outer electrode. an insulating bodyinserted in and projecting from the said casing and having an axial bore, a metal pin extending through said bore and forming the inner electrode, said insulating body consisting of a plurality of metal inserts embedded in a compressed substance composed of powdered in-.

, the said casing and having an axial bore, a metal pin extending. through said bore and forming the inner electrode, a sleeve of a material of high heat conductivity slipped on to the projecting end and forming an enlarged radiating surface, said in-. sulating body consisting of an electrically insulating mass with good conductors of heat extending therethrough, said conductors being separated both from the pin and from one another by the insulating mass and forming a continuous connection between the base and the said radiating sleeve. o

l4. A spark plug, comprising in combination a'metal casing forming the outer electrode, an insulating body inserted in and projecting from the said casing and having an axial bore, a metal pin extending through'said bore and forming the inner electrode, and an aluminium sleeve having an electrically oxidized surface slipped on to the projecting end and forming an enlarged radiating surface, said insulating body consisting of an electrically insulatingmass with good conductors of heat extending therethrough, said conductors being separated both from the pin and. r

metal casing forming the outer electrode, an insulating body inserted in and projecting from the said casing and having an axial bore, a metal pin extending through said bore and forming the inner electrode, a sleeve of a material of high heat conductivity slipped on to the projecting end and forming an enlarged radiating surface, said insulating body composed of a closely wound band of mica having metal strips mutually displaced on its two sides, said strips being separated both from the pin and from one another by the band of mica and forming a continuous connection between the base and the said radiating sleeve.

16. A spark plug, comprising in combination a metal casing forming the outer electrode, an insulating body inserted in and projecting from said casing and having an axial bore, a metal pin extendingthrough said bore and forming the inner electrode, a sleeve of a material of high heat conductivity slipped on to the projecting end and forming an enlarged radiating surface,

' said insulating body composed of a closely wound band of mica having aluminium strips with ele'ctrically oxidized surfaces, said strips being separated both from the pin and from one another by the band of mica and forming a continuous connection between the base and the said radiating sleeve.

HERMANN GEORG BORNEMANN. 

